Power devices using Si are currently being developed for high frequency, high power control, and there has been a growing trend to achieve higher performances through various structural contrivances, which are approaching theoretical limits. Power devices must often operate in adverse environments subject to high temperatures, radiation, etc., and such devices cannot be produced with Si. New materials are therefore necessary to attain higher performance. Because it has a broad forbidden bandwidth of 2.93 eV in 6H-type, SiC provides superior electrical conductivity control and radiation resistance at high temperatures; its dielectric breakdown field of one order of magnitude greater than that of Si enables its use in high-voltage devices; and because the saturation drift speed of the electrons are approximately twice that of Si, SiC can be used as a semiconductor material with high frequency, high power control.
When SiC, with its superior characteristics, is used in power devices, Ni is used for the ohmic contact electrodes on n-type SiC. However, using vacuum deposition methods to deposit Ni only on n-type SiC creates a Schottky barrier at the interface between the metal and the semiconductor, producing rectification characteristics and preventing ohmicity. Heat treatment accelerates diffusion of Ni throughout the SiC and, inversely, Si or C contained in SiC throughout the Ni, producing ohmic contact electrodes for the first time. One drawback is that it is necessary to administer heat treatment at temperatures above 1,000.degree. C. to achieve diffusion. Other drawbacks are that during heat treatment, the Ni and Si from SiC diffuse into each other forming nickel silicide, and C contained in SiC diffuses to the surface of the Ni electrodes to precipitate as graphite, as described on page 567 of Mat. Res. Soc. Symp. Proc. Vol. 242 (1992), (J. B. Petit et al), or the Ni continues to diffuse into the SiC due to extended application of high temperature, thereby increasing contact resistance of the electrodes.
It is an object of the invention to eliminate these defects by providing a method of manufacturing SiC electronic devices that can prevent the reciprocal diffusion of Ni in the electrodes with the Si or C contained in the SiC.